To be perfecly fair, from my relatively brief poly experience, there is also the other half of the coin: the disappointment of not being the one said partner choses, the potential jealousy (irrational, but, undenyably not exactly an emotion that can be controlled at will), and, as Alicorn's post highlighted, the fear of losing said partner -breakups do happen, and, in relation to another post, the situation between a mother and her sons is quite different because that bond does not fit this particular requirement-.